1. Field of the Invention
This invention relates to a device for automatically focusing a lens in a camera, and more particularly to a device for automatically adjusting the focus of an image formed by an objective in a photographic or cinematographic camera. This invention further relates to a device for indicating the position where an image is focused by an objective to facilitate the focusing of an image in a camera.
2. Description of the Prior Art
In a conventional camera, the position at which an image is focused is visually determined by the photographer who adjusts the focus by manually operating a focusing lens. This requires high degree of skill and good eyesight. Therefore, it has been desired that the focusing operation of a camera be automatically conducted by use of automatic focusing means. Various attempts have been made to automatically focus an image in a camera. The conventionally known means for automatic focus control employs a photodetector on which the image to be focus-controlled is formed and utilizes the output from the photodetector which shows the maximum value when the image is best focused.
The above described conventional automatic focus control means has a defect in that the response is slow. Particularly when the scene is dark, the photodetector is required to have very fast response and high sensitivity. Further, since in the conventional automatic focus control means any fluctuation in the quantity of light received by the photodetector constitutes noise in the output from the photodetector, it is difficult to precisely detect the focus and control the lens.